.banner-img{
    width:100%;
    height: 600px;
    background-size: cover;
}
.banner{
    height: 600px;
    width: 100%;
    margin-top: 20px;
}

@media (max-width:768px){
    .banner-img{
        height: 300px;
    }
    .banner{
        height: 300px;
    }
}